Monday, January 17, 2011

Jet lag

With certainty, human beings never travelled much more than 10 km in a day throughout human evolution. Even 30 years ago, you could easily find adults who had never been in a plane in their life. Now, I have children in their early 20s who have been to more countries than I have.

In 1966 I was booted out of London and sent off to live in Adelaide, South Australia. The flight was London, Frankfurt, Athens, Cairo, Karachi, Singapore, Sydney, Melbourne, Adelaide. That’s eight legs for a flight that has two legs now and only one in 2020. I don’t recall getting jet lag, probably because the trip took so long (you disembarked and pfaffed around at each airport; no shopping malls).

Circadian disrhythmia

Travelling across time zones now is rapid and will upset your circadian rhythm (from circa diem, Latin for “about 24 hours”). More than 300 bodily functions occur with a 24 hour rhythm. These functions normally have “high” and “low' points during the 24 hour period, corresponding to a sleep-wake cycle. For example, body temperature, (which peaks at around 6 pm), heart rate, (which is higher in the afternoon), and the stomach, (which empties a little more quickly in the morning than in the evening) all have a circadian rhythm.

Adjusting body clock

When travelling across time zones, some people adjust their body clocks to their destination time in the two or three days before departure. On arrival they can quickly adopt local times for eating and sleeping. This can be very effective when crossing 1-4 time zones. For example, if you are travelling east, gradually get up earlier each morning so that you are 1-2 hours “closer” to your destination time zone.

Getting sunlight early in the morning also helps this transition. Do the reverse if you are travelling west. Adjust to getting up later before you leave and expose yourself to bright sunlight in the evening if possible so that your body feels like it is closer to your destination time zone.

Anything you can do food-wise?

Yes, but it is going to sound a bit obvious. Some folk pre-order a vegetarian or low-fat dish, not because they are necessarily vego or weight conscious, it’s just that the “special meals” are often better quality. Besides, fatty meals can make you feel a bit gluggy. It’s not as if you can go for a long walk afterwards to feel more normal.

The humidity in aircraft is around 10-15%, which means that moisture is lost from your body a bit quicker than normal, estimated at an extra 20-25 mL per hour. I have read that new aircraft will have a higher humidity because anecdotal feedback has been that people experience less jet lag at a more normal humidity of 25-30%. Anyway, this is the reason you are told to “keep up your fluids” when flying. That includes tea and coffee (caffeine does not cause excessive fluid loss), water and juice.

It doesn’t include alcohol. I don’t drink alcohol on flights for two reasons: 1) it is dehydrating; and 2) my wine tastes dreadful in a dry atmosphere from a plastic cup (yeah, I know, you travel business class and get a very nice red in a glass, so it doesn’t apply). One advantage of having a beer or wine with your airline meal is that alcohol reduces platelet aggregability so blood is less sticky and you have less chance of deep vein thrombosis.

What does it all mean?

Most people jump on a plane, cross a few time zones, then cruise straight into local time. That’s probably the best you can do when crossing four or more time zones and on holidays. With three or less time zones, I like to pre-adjust my body clock in the preceding days at one hour a day, especially for easterly travel. When you arrive, immediately adopt the local time, try not to nap during the day to catch up sleep, and sleep in a cool bedroom. It can be helpful to go for a walk three hours or so before bedtime for a more restful sleep. Despite all the theories, the best cure for jet lag is still time. I think that being fit and eating sensibly helps.

Final tip – get to the airport early. The last thing you want to get is a middle seat. Sorry. Forgot. You travel business class.

Reference: Journal of Sports Sciences 2007; 25 (S1): S125-S134

Sunday, January 9, 2011

Vitamin C

Vitamin C became famous the moment that Linus Pauling (pictured), a US professor of chemistry, said he thought that vitamin C could reduce the risk of the common cold. By this time, in the early 1970s, he had already pocketed two Nobel Prizes in chemistry and peace. He could have got a third when he was working hard to determine the structure of DNA before Watson and Crick beat him to it. So, Pauling was a bloke to whom you should lend an ear.

Early reports promising

Although vitamin C (ascorbic acid) wasn’t first isolated, or “discovered”, until 1928, for many years we knew of a vague compound that stopped you from getting scurvy. Only 10 mg a day will keep scurvy away, yet there has been long conjecture that a whole lot more than 10 mg was needed each day to be healthy. Not that long ago we found that people with high levels of vitamin C in their blood had a lower risk of heart disease and early death. Unfortunately, when we started giving people vitamin C supplements the results were less exciting.

You’ve heard me say this a few times - just because there is an association, we should never assume we are seeing cause and effect. High blood vitamin C is probably a “marker” of a lifestyle that includes plenty of fruit and vegetables, and of course, if you eat your veggies then there is a reasonable chance you don’t smoke or drink gallons of alcohol, and probably walk the dog too. Less heart disease was more likely due to good living than being able to pin it on a single vitamin like ascorbic acid.

Vitamin C alone not that useful

There is also a good chance that any one vitamin can’t do a lot on its own to prevent disease and needs a whole range of other nutrients and antioxidants alongside it before a benefit kicks in.

In a new review of vitamin C, published in the British Journal of Nutrition, it states that: “It should be acknowledged that in the epidemiological studies on the relationship between vitamin C concentrations and diseases there is no evidence that the relationship is due to vitamin C itself.”

Although it has long been trendy to pop 500 mg tablets of vitamin C, there is a limit to how much vitamin C our body can store. Once we have over 200 mg a day our body becomes “saturated” with vitamin C and any over this amount ends up in the loo.

And the common cold?

The Cochrane Database [ Systematic Review] in 2007 said: “The failure of vitamin C supplementation to reduce the incidence of colds in the normal population indicates that routine mega-dose prophylaxis is not rationally justified for community use.”

And when the most powerful database in the universe says that, you better take notice. Hey, Linus was a legend and even legends are allowed to speculate and not get it right sometimes. Remember, his first crack at the DNA structure was wrong too. A brilliant human, but still a human.

What does it all mean?

The daily vitamin C recommendations in Australia and New Zealand are 45 mg; 75-90 mg in the US; and 40 mg in the UK. If you can eat an orange (70mg), a small salad (100 mg), a serve of broccoli (30mg if you don’t boil it to a fraction from mush), or a banana (12 mg) you can see that it is pretty easy to meet your C needs with normal good eating. If you have a very low vitamin C status (more likely in smokers) then you might benefit from a supplement (100 mg, not 500 mg or 1000 mg), but as I, and many others in the nutrition game, will tell you, a vitamin supplement ain’t no substitute for getting decent feed into you.

Reference: British Journal of Nutrition 2010; 103: 1251-1259